In machine tools and other similar equipment, it is frequently necessary to use hydraulically-powered elements such as cylinders, hydraulic motors, hydraulic clutch assemblies and the like, and, as many such elements are contained with a machine housing, leakage and design drainage are often channeled to a common reservoir. In order to relieve the fluid build-up, a gravity drain line is often provided between the housing and a hydraulic tank assembly.
In some assemblies, however, it is impractical or impossible to provide a gravity drain system. For example, the size of a drain line may have to be considerably large to properly drain high volumes solely under the influence of gravity. Further, it may be impossible to provide a gravity drain where the exit line must travel uphill to a head above the reservoir level, as is frequently encountered in vertically movable machine assemblies wherein the fluid lines are often looped to accommodate vertical movement. In this latter type of assembly, a scavenger pump is frequently employed to get the drain oils back to the hydraulic tank.
Several prior art assemblies has been designed to scavenge a vertically movable assembly, and most generally employ a float which moves with the fluid level. However, it must be realized that the bouyant force on a relatively small float may not be significant, and is often not directly usable to move a mechanical element. Therefore, assemblies which must move mechanical elements by float means frequently may employ a force magnifying linkage to shift a spool and actuate some sort of switch which in turn, activates a motor and pump assembly. The float switch, well-known in the art, serves to close electrical contacts and power an electrical motor which in turn drives a hydraulic pump. The electrical motors in the range of one horse power or so, are quite bulky and heavy, and are cumbersome to fit into a design. Further, the electrical motor/hydraulic pump arrangement is binary in nature; that is, the pump runs at one speed for a predetermined amount of time and then shuts off, possibly causing the pump to run dry. The additional necessary electrical elements, such as relay logic in a magnetic panel, contribute to the expense of the system.
The prior art assembly falls short of solving the ideal condition, that is, attempting to match exit flow rate from the reservoir to varying inlet flow rates to the reservoir, with a relatively small, compact group of parts.
Applicant has obviated the difficulties inherent in the prior art assembly by a scavenger pump which is controlled by a fluid control valve assembly and powered solely by a hydraulic motor. The system has variable pumping rates in accordance with varying fluid levels of the reservoir, attempting to match the two.
It is therefore an object of the present invention to provide a scavenger pump assembly which tends to substantially match reservoir inlet and exit flow rates.
Another object of the present invention is to provide a fluid control valve for controlling a scavenger pump assembly having a relatively simple non-linkage float system having a design which can generally fit into a space less than that of an equivalent linkage-type design.